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Real Estate and Accumulated Depreciation (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Real Estate Properties [Line Items]        
Initial basis $ 863,513      
Cost capitalized subsequent to acquisition 837,300      
Basis at close of period, land 422,546      
Basis at close of period, building and improvements 1,278,267      
Basis at close of period, leasehold interests 0      
Total 1,700,813 $ 1,622,710 $ 1,560,159 $ 1,459,439
Accumulated depreciation 458,279 425,370 $ 396,617 $ 364,663
Book value 1,242,534 1,197,340    
Related debt 783,400 796,169    
Development land, related debt 68,672 $ 43,641    
Total, related debt 858,774      
Shopping Centers        
Real Estate Properties [Line Items]        
Initial basis 760,099      
Cost capitalized subsequent to acquisition 401,402      
Basis at close of period, land 384,647      
Basis at close of period, building and improvements 776,854      
Basis at close of period, leasehold interests 0      
Total 1,161,501      
Accumulated depreciation 316,158      
Book value 845,343      
Related debt 621,113      
Shopping Centers | Ashburn Village, Ashburn, VA        
Real Estate Properties [Line Items]        
Initial basis 11,431      
Cost capitalized subsequent to acquisition 20,159      
Basis at close of period, land 6,764      
Basis at close of period, building and improvements 24,826      
Basis at close of period, leasehold interests 0      
Total 31,590      
Accumulated depreciation 12,247      
Book value 19,343      
Related debt $ 28,822      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Ashland Square Phase I, Dumfries, VA        
Real Estate Properties [Line Items]        
Initial basis $ 1,178      
Cost capitalized subsequent to acquisition 7,503      
Basis at close of period, land 1,178      
Basis at close of period, building and improvements 7,503      
Basis at close of period, leasehold interests 0      
Total 8,681      
Accumulated depreciation 1,440      
Book value 7,241      
Related debt $ 0      
Shopping Centers | Ashland Square Phase I, Dumfries, VA | Minimum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 20 years      
Shopping Centers | Ashland Square Phase I, Dumfries, VA | Maximum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Beacon Center, Alexandria, VA        
Real Estate Properties [Line Items]        
Initial basis $ 24,161      
Cost capitalized subsequent to acquisition 18,402      
Basis at close of period, land 22,668      
Basis at close of period, building and improvements 19,895      
Basis at close of period, leasehold interests 0      
Total 42,563      
Accumulated depreciation 13,721      
Book value 28,842      
Related debt $ 41,753      
Shopping Centers | Beacon Center, Alexandria, VA | Minimum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Beacon Center, Alexandria, VA | Maximum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | BJ’s Wholesale Club, Alexandria, VA        
Real Estate Properties [Line Items]        
Initial basis $ 22,623      
Cost capitalized subsequent to acquisition 0      
Basis at close of period, land 22,623      
Basis at close of period, building and improvements 0      
Basis at close of period, leasehold interests 0      
Total 22,623      
Accumulated depreciation 0      
Book value 22,623      
Related debt $ 11,129      
Buildings and Improvements Depreciable Lives in Years 0 years      
Shopping Centers | Boca Valley Plaza, Boca Raton, FL        
Real Estate Properties [Line Items]        
Initial basis $ 16,720      
Cost capitalized subsequent to acquisition 1,616      
Basis at close of period, land 5,735      
Basis at close of period, building and improvements 12,601      
Basis at close of period, leasehold interests 0      
Total 18,336      
Accumulated depreciation 4,279      
Book value 14,057      
Related debt $ 10,277      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Boulevard, Fairfax, VA        
Real Estate Properties [Line Items]        
Initial basis $ 4,883      
Cost capitalized subsequent to acquisition 4,461      
Basis at close of period, land 3,687      
Basis at close of period, building and improvements 5,657      
Basis at close of period, leasehold interests 0      
Total 9,344      
Accumulated depreciation 2,594      
Book value 6,750      
Related debt $ 17,207      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Briggs Chaney MarketPlace, Silver Spring, MD        
Real Estate Properties [Line Items]        
Initial basis $ 27,037      
Cost capitalized subsequent to acquisition 3,806      
Basis at close of period, land 9,789      
Basis at close of period, building and improvements 21,054      
Basis at close of period, leasehold interests 0      
Total 30,843      
Accumulated depreciation 7,249      
Book value 23,594      
Related debt $ 14,325      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Broadlands Village, Ashburn, VA        
Real Estate Properties [Line Items]        
Initial basis $ 5,316      
Cost capitalized subsequent to acquisition 27,392      
Basis at close of period, land 5,300      
Basis at close of period, building and improvements 27,408      
Basis at close of period, leasehold interests 0      
Total 32,708      
Accumulated depreciation 9,954      
Book value 22,754      
Related debt $ 17,050      
Shopping Centers | Broadlands Village, Ashburn, VA | Minimum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Broadlands Village, Ashburn, VA | Maximum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Countryside Marketplace, Sterling, VA        
Real Estate Properties [Line Items]        
Initial basis $ 28,912      
Cost capitalized subsequent to acquisition 3,712      
Basis at close of period, land 7,666      
Basis at close of period, building and improvements 24,958      
Basis at close of period, leasehold interests 0      
Total 32,624      
Accumulated depreciation 8,012      
Book value 24,612      
Related debt $ 14,335      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Cranberry Square, Westminster, MD        
Real Estate Properties [Line Items]        
Initial basis $ 31,578      
Cost capitalized subsequent to acquisition 635      
Basis at close of period, land 6,700      
Basis at close of period, building and improvements 25,513      
Basis at close of period, leasehold interests 0      
Total 32,213      
Accumulated depreciation 3,408      
Book value 28,805      
Related debt $ 17,630      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Cruse MarketPlace, Cumming, GA        
Real Estate Properties [Line Items]        
Initial basis $ 12,226      
Cost capitalized subsequent to acquisition 369      
Basis at close of period, land 3,901      
Basis at close of period, building and improvements 8,694      
Basis at close of period, leasehold interests 0      
Total 12,595      
Accumulated depreciation 2,793      
Book value 9,802      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Flagship Center, Rockville, MD        
Real Estate Properties [Line Items]        
Initial basis $ 160      
Cost capitalized subsequent to acquisition 9      
Basis at close of period, land 169      
Basis at close of period, building and improvements 0      
Basis at close of period, leasehold interests 0      
Total 169      
Accumulated depreciation 0      
Book value 169      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 0 years      
Shopping Centers | French Market, Oklahoma City, OK        
Real Estate Properties [Line Items]        
Initial basis $ 5,781      
Cost capitalized subsequent to acquisition 13,790      
Basis at close of period, land 1,118      
Basis at close of period, building and improvements 18,453      
Basis at close of period, leasehold interests 0      
Total 19,571      
Accumulated depreciation 10,629      
Book value 8,942      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Germantown, Germantown, MD        
Real Estate Properties [Line Items]        
Initial basis $ 2,034      
Cost capitalized subsequent to acquisition 567      
Basis at close of period, land 2,034      
Basis at close of period, building and improvements 567      
Basis at close of period, leasehold interests 0      
Total 2,601      
Accumulated depreciation 241      
Book value 2,360      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | The Glen, Woodbridge, VA        
Real Estate Properties [Line Items]        
Initial basis $ 12,918      
Cost capitalized subsequent to acquisition 7,767      
Basis at close of period, land 5,300      
Basis at close of period, building and improvements 15,385      
Basis at close of period, leasehold interests 0      
Total 20,685      
Accumulated depreciation 8,498      
Book value 12,187      
Related debt $ 8,172      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Great Eastern, District Heights, MD        
Real Estate Properties [Line Items]        
Initial basis $ 4,993      
Cost capitalized subsequent to acquisition 10,678      
Basis at close of period, land 3,785      
Basis at close of period, building and improvements 11,886      
Basis at close of period, leasehold interests 0      
Total 15,671      
Accumulated depreciation 8,293      
Book value 7,378      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Great Falls Center, Great Falls, VA        
Real Estate Properties [Line Items]        
Initial basis $ 41,750      
Cost capitalized subsequent to acquisition 3,113      
Basis at close of period, land 14,766      
Basis at close of period, building and improvements 30,097      
Basis at close of period, leasehold interests 0      
Total 44,863      
Accumulated depreciation 6,802      
Book value 38,061      
Related debt $ 13,401      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Hampshire Langley, Takoma, MD        
Real Estate Properties [Line Items]        
Initial basis $ 3,159      
Cost capitalized subsequent to acquisition 3,394      
Basis at close of period, land 1,856      
Basis at close of period, building and improvements 4,697      
Basis at close of period, leasehold interests 0      
Total 6,553      
Accumulated depreciation 3,604      
Book value 2,949      
Related debt $ 16,352      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Hunt Club Corners, Apopka, FL        
Real Estate Properties [Line Items]        
Initial basis $ 12,584      
Cost capitalized subsequent to acquisition 3,831      
Basis at close of period, land 4,822      
Basis at close of period, building and improvements 11,593      
Basis at close of period, leasehold interests 0      
Total 16,415      
Accumulated depreciation 3,343      
Book value 13,072      
Related debt $ 5,809      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Jamestown Place, Altamonte Springs, FL        
Real Estate Properties [Line Items]        
Initial basis $ 14,055      
Cost capitalized subsequent to acquisition 1,174      
Basis at close of period, land 4,455      
Basis at close of period, building and improvements 10,774      
Basis at close of period, leasehold interests 0      
Total 15,229      
Accumulated depreciation 3,153      
Book value 12,076      
Related debt $ 7,685      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Kentlands Square I, Gaithersburg, MD        
Real Estate Properties [Line Items]        
Initial basis $ 14,379      
Cost capitalized subsequent to acquisition 328      
Basis at close of period, land 5,006      
Basis at close of period, building and improvements 9,701      
Basis at close of period, leasehold interests 0      
Total 14,707      
Accumulated depreciation 3,460      
Book value 11,247      
Related debt $ 6,813      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Kentlands Square II, Gaithersburg, MD        
Real Estate Properties [Line Items]        
Initial basis $ 76,723      
Cost capitalized subsequent to acquisition 1,327      
Basis at close of period, land 22,800      
Basis at close of period, building and improvements 55,250      
Basis at close of period, leasehold interests 0      
Total 78,050      
Accumulated depreciation 7,503      
Book value 70,547      
Related debt $ 37,701      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Kentlands Place, Gaithersburg, MD        
Real Estate Properties [Line Items]        
Initial basis $ 1,425      
Cost capitalized subsequent to acquisition 7,220      
Basis at close of period, land 1,425      
Basis at close of period, building and improvements 7,220      
Basis at close of period, leasehold interests 0      
Total 8,645      
Accumulated depreciation 3,446      
Book value 5,199      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Lansdowne Town Center, Leesburg, VA        
Real Estate Properties [Line Items]        
Initial basis $ 6,545      
Cost capitalized subsequent to acquisition 36,813      
Basis at close of period, land 6,546      
Basis at close of period, building and improvements 36,812      
Basis at close of period, leasehold interests 0      
Total 43,358      
Accumulated depreciation 12,546      
Book value 30,812      
Related debt $ 33,571      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Leesburg Pike Plaza, Baileys Crossroads, VA        
Real Estate Properties [Line Items]        
Initial basis $ 2,418      
Cost capitalized subsequent to acquisition 6,243      
Basis at close of period, land 1,132      
Basis at close of period, building and improvements 7,529      
Basis at close of period, leasehold interests 0      
Total 8,661      
Accumulated depreciation 5,815      
Book value 2,846      
Related debt $ 15,917      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Lumberton Plaza, Lumberton, NJ        
Real Estate Properties [Line Items]        
Initial basis $ 4,400      
Cost capitalized subsequent to acquisition 11,170      
Basis at close of period, land 950      
Basis at close of period, building and improvements 14,620      
Basis at close of period, leasehold interests 0      
Total 15,570      
Accumulated depreciation 12,431      
Book value 3,139      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Metro Pike Center, Rockville, MD        
Real Estate Properties [Line Items]        
Initial basis $ 33,123      
Cost capitalized subsequent to acquisition 3,760      
Basis at close of period, land 26,064      
Basis at close of period, building and improvements 10,819      
Basis at close of period, leasehold interests 0      
Total 36,883      
Accumulated depreciation 1,172      
Book value 35,711      
Related debt $ 14,482      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Shops at Monocacy, Frederick, MD        
Real Estate Properties [Line Items]        
Initial basis $ 9,541      
Cost capitalized subsequent to acquisition 13,926      
Basis at close of period, land 9,260      
Basis at close of period, building and improvements 14,207      
Basis at close of period, leasehold interests 0      
Total 23,467      
Accumulated depreciation 5,101      
Book value 18,366      
Related debt $ 12,725      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Northrock, Warrenton, VA        
Real Estate Properties [Line Items]        
Initial basis $ 12,686      
Cost capitalized subsequent to acquisition 15,217      
Basis at close of period, land 12,686      
Basis at close of period, building and improvements 15,217      
Basis at close of period, leasehold interests 0      
Total 27,903      
Accumulated depreciation 3,343      
Book value 24,560      
Related debt $ 15,357      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Olde Forte Village, Ft. Washington, MD        
Real Estate Properties [Line Items]        
Initial basis $ 15,933      
Cost capitalized subsequent to acquisition 6,575      
Basis at close of period, land 5,409      
Basis at close of period, building and improvements 17,099      
Basis at close of period, leasehold interests 0      
Total 22,508      
Accumulated depreciation 6,639      
Book value 15,869      
Related debt $ 10,372      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Olney, Olney, MD        
Real Estate Properties [Line Items]        
Initial basis $ 1,884      
Cost capitalized subsequent to acquisition 1,792      
Basis at close of period, land 0      
Basis at close of period, building and improvements 3,676      
Basis at close of period, leasehold interests 0      
Total 3,676      
Accumulated depreciation 3,259      
Book value 417      
Related debt $ 11,446      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Orchard Park, Dunwoody, GA        
Real Estate Properties [Line Items]        
Initial basis $ 19,377      
Cost capitalized subsequent to acquisition 950      
Basis at close of period, land 7,751      
Basis at close of period, building and improvements 12,576      
Basis at close of period, leasehold interests 0      
Total 20,327      
Accumulated depreciation 3,064      
Book value 17,263      
Related debt $ 10,253      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Palm Springs Center, Altamonte Springs, FL        
Real Estate Properties [Line Items]        
Initial basis $ 18,365      
Cost capitalized subsequent to acquisition 1,393      
Basis at close of period, land 5,739      
Basis at close of period, building and improvements 14,019      
Basis at close of period, leasehold interests 0      
Total 19,758      
Accumulated depreciation 4,128      
Book value 15,630      
Related debt $ 8,697      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Ravenwood, Baltimore, MD        
Real Estate Properties [Line Items]        
Initial basis $ 1,245      
Cost capitalized subsequent to acquisition 4,175      
Basis at close of period, land 703      
Basis at close of period, building and improvements 4,717      
Basis at close of period, leasehold interests 0      
Total 5,420      
Accumulated depreciation 2,922      
Book value 2,498      
Related debt $ 14,961      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | 11503 Rockville Pike/5541 Nicholson Lane, Rockville, MD        
Real Estate Properties [Line Items]        
Initial basis $ 26,561      
Cost capitalized subsequent to acquisition 0      
Basis at close of period, land 22,113      
Basis at close of period, building and improvements 4,448      
Basis at close of period, leasehold interests 0      
Total 26,561      
Accumulated depreciation 695      
Book value 25,866      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | 1500/1580/1582/1584 Rockville Pike, Rockville, MD        
Real Estate Properties [Line Items]        
Initial basis $ 51,149      
Cost capitalized subsequent to acquisition 1,093      
Basis at close of period, land 43,863      
Basis at close of period, building and improvements 8,379      
Basis at close of period, leasehold interests 0      
Total 52,242      
Accumulated depreciation 4,605      
Book value 47,637      
Related debt 0      
Shopping Centers | Seabreeze Plaza, Palm Harbor, FL        
Real Estate Properties [Line Items]        
Initial basis 24,526      
Cost capitalized subsequent to acquisition 1,539      
Basis at close of period, land 8,665      
Basis at close of period, building and improvements 17,400      
Basis at close of period, leasehold interests 0      
Total 26,065      
Accumulated depreciation 5,079      
Book value 20,986      
Related debt $ 16,543      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Market Place at Sea Colony, Bethany Beach, DE        
Real Estate Properties [Line Items]        
Initial basis $ 2,920      
Cost capitalized subsequent to acquisition 170      
Basis at close of period, land 1,147      
Basis at close of period, building and improvements 1,943      
Basis at close of period, leasehold interests 0      
Total 3,090      
Accumulated depreciation 429      
Book value 2,661      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Seven Corners, Falls Church, VA        
Real Estate Properties [Line Items]        
Initial basis $ 4,848      
Cost capitalized subsequent to acquisition 44,062      
Basis at close of period, land 4,913      
Basis at close of period, building and improvements 43,997      
Basis at close of period, leasehold interests 0      
Total 48,910      
Accumulated depreciation 27,710      
Book value 21,200      
Related debt $ 66,210      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Severna Park Marketplace, Severna Park, MD        
Real Estate Properties [Line Items]        
Initial basis $ 63,254      
Cost capitalized subsequent to acquisition 92      
Basis at close of period, land 12,700      
Basis at close of period, building and improvements 50,646      
Basis at close of period, leasehold interests 0      
Total 63,346      
Accumulated depreciation 6,651      
Book value 56,695      
Related debt $ 33,097      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Shops at Fairfax, Fairfax, VA        
Real Estate Properties [Line Items]        
Initial basis $ 2,708      
Cost capitalized subsequent to acquisition 9,923      
Basis at close of period, land 992      
Basis at close of period, building and improvements 11,639      
Basis at close of period, leasehold interests 0      
Total 12,631      
Accumulated depreciation 7,627      
Book value 5,004      
Related debt $ 11,472      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | Smallwood Village Center, Waldorf, MD        
Real Estate Properties [Line Items]        
Initial basis $ 17,819      
Cost capitalized subsequent to acquisition 7,662      
Basis at close of period, land 6,402      
Basis at close of period, building and improvements 19,079      
Basis at close of period, leasehold interests 0      
Total 25,481      
Accumulated depreciation 6,492      
Book value 18,989      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Southdale, Glen Burnie, MD        
Real Estate Properties [Line Items]        
Initial basis $ 18,895      
Cost capitalized subsequent to acquisition 22,684      
Basis at close of period, land 15,245      
Basis at close of period, building and improvements 26,334      
Basis at close of period, leasehold interests 0      
Total 41,579      
Accumulated depreciation 20,763      
Book value 20,816      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Southside Plaza, Richmond, VA        
Real Estate Properties [Line Items]        
Initial basis $ 6,728      
Cost capitalized subsequent to acquisition 10,647      
Basis at close of period, land 1,878      
Basis at close of period, building and improvements 15,497      
Basis at close of period, leasehold interests 0      
Total 17,375      
Accumulated depreciation 11,910      
Book value 5,465      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | South Dekalb Plaza, Atlanta, GA        
Real Estate Properties [Line Items]        
Initial basis $ 2,474      
Cost capitalized subsequent to acquisition 4,186      
Basis at close of period, land 703      
Basis at close of period, building and improvements 5,957      
Basis at close of period, leasehold interests 0      
Total 6,660      
Accumulated depreciation 4,658      
Book value 2,002      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Thruway, Winston-Salem, NC        
Real Estate Properties [Line Items]        
Initial basis $ 7,848      
Cost capitalized subsequent to acquisition 23,925      
Basis at close of period, land 7,692      
Basis at close of period, building and improvements 24,081      
Basis at close of period, leasehold interests 0      
Total 31,773      
Accumulated depreciation 15,673      
Book value 16,100      
Related debt $ 39,213      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Village Center, Centreville, VA        
Real Estate Properties [Line Items]        
Initial basis $ 16,502      
Cost capitalized subsequent to acquisition 2,354      
Basis at close of period, land 7,851      
Basis at close of period, building and improvements 11,005      
Basis at close of period, leasehold interests 0      
Total 18,856      
Accumulated depreciation 6,346      
Book value 12,510      
Related debt $ 13,832      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Westview Village, Frederick, MD        
Real Estate Properties [Line Items]        
Initial basis $ 6,047      
Cost capitalized subsequent to acquisition 24,230      
Basis at close of period, land 6,047      
Basis at close of period, building and improvements 24,230      
Basis at close of period, leasehold interests 0      
Total 30,277      
Accumulated depreciation 6,422      
Book value 23,855      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 50 years      
Shopping Centers | White Oak, Silver Spring, MD        
Real Estate Properties [Line Items]        
Initial basis $ 6,277      
Cost capitalized subsequent to acquisition 5,357      
Basis at close of period, land 4,649      
Basis at close of period, building and improvements 6,985      
Basis at close of period, leasehold interests 0      
Total 11,634      
Accumulated depreciation 5,906      
Book value 5,728      
Related debt $ 24,504      
Buildings and Improvements Depreciable Lives in Years 40 years      
Shopping Centers | Other Buildings / Improvements        
Real Estate Properties [Line Items]        
Cost capitalized subsequent to acquisition $ 211      
Basis at close of period, building and improvements 211      
Total 211      
Accumulated depreciation 103      
Book value 108      
Related debt $ 0      
Shopping Centers | North Glebe Road, Arlington, VA | Minimum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 2 years      
Shopping Centers | North Glebe Road, Arlington, VA | Maximum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 3 years      
Mixed-Use Properties        
Real Estate Properties [Line Items]        
Initial basis $ 43,967      
Cost capitalized subsequent to acquisition 427,719      
Basis at close of period, land 28,496      
Basis at close of period, building and improvements 443,190      
Basis at close of period, leasehold interests 0      
Total 471,686      
Accumulated depreciation 142,121      
Book value 329,565      
Related debt $ 237,661      
Mixed-Use Properties | 1500/1580/1582/1584 Rockville Pike, Rockville, MD | Acquisition Date One        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 5 years      
Mixed-Use Properties | 1500/1580/1582/1584 Rockville Pike, Rockville, MD | Acquisition Date Two        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 10 years      
Mixed-Use Properties | 1500/1580/1582/1584 Rockville Pike, Rockville, MD | Acquisition Date Three        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 5 years      
Mixed-Use Properties | 1500/1580/1582/1584 Rockville Pike, Rockville, MD | Acquisition Date Four        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 4 years      
Mixed-Use Properties | Avenel Business Park, Gaithersburg, MD        
Real Estate Properties [Line Items]        
Initial basis $ 21,459      
Cost capitalized subsequent to acquisition 30,504      
Basis at close of period, land 3,756      
Basis at close of period, building and improvements 48,207      
Basis at close of period, leasehold interests 0      
Total 51,963      
Accumulated depreciation 35,261      
Book value 16,702      
Related debt $ 28,945      
Mixed-Use Properties | Avenel Business Park, Gaithersburg, MD | Minimum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 35 years      
Mixed-Use Properties | Avenel Business Park, Gaithersburg, MD | Maximum        
Real Estate Properties [Line Items]        
Buildings and Improvements Depreciable Lives in Years 40 years      
Mixed-Use Properties | Clarendon Center, Arlington, VA        
Real Estate Properties [Line Items]        
Initial basis [1] $ 12,753      
Cost capitalized subsequent to acquisition [1] 185,436      
Basis at close of period, land [1] 16,287      
Basis at close of period, building and improvements [1] 181,902      
Basis at close of period, leasehold interests [1] 0      
Total [1] 198,189      
Accumulated depreciation [1] 32,314      
Book value [1] 165,875      
Related debt [1] $ 109,144      
Buildings and Improvements Depreciable Lives in Years 50 years      
Mixed-Use Properties | 601 Pennsylvania Ave., Washington, DC        
Real Estate Properties [Line Items]        
Initial basis $ 5,479      
Cost capitalized subsequent to acquisition 66,158      
Basis at close of period, land 5,667      
Basis at close of period, building and improvements 65,970      
Basis at close of period, leasehold interests 0      
Total 71,637      
Accumulated depreciation 49,856      
Book value 21,781      
Related debt $ 0      
Buildings and Improvements Depreciable Lives in Years 35 years      
Mixed-Use Properties | Washington Square, Alexandria, VA        
Real Estate Properties [Line Items]        
Initial basis $ 2,034      
Cost capitalized subsequent to acquisition 54,945      
Basis at close of period, land 544      
Basis at close of period, building and improvements 56,435      
Basis at close of period, leasehold interests 0      
Total 56,979      
Accumulated depreciation 22,859      
Book value 34,120      
Related debt $ 29,428      
Buildings and Improvements Depreciable Lives in Years 50 years      
Development Land        
Real Estate Properties [Line Items]        
Initial basis $ 59,447      
Cost capitalized subsequent to acquisition 8,179      
Basis at close of period, land 9,403      
Basis at close of period, building and improvements 58,223      
Basis at close of period, leasehold interests 0      
Total 67,626      
Accumulated depreciation 0      
Book value 67,626      
Development land, related debt 0      
Development Land | Park Van Ness, Washington, DC        
Real Estate Properties [Line Items]        
Initial basis 2,242      
Cost capitalized subsequent to acquisition 90,676      
Basis at close of period, land 2,242      
Basis at close of period, building and improvements 90,676      
Basis at close of period, leasehold interests 0      
Total 92,918      
Accumulated depreciation 1,831      
Book value 91,087      
Development land, related debt 70,144      
Development Land | Ashland Square Phase II, Manassas, VA        
Real Estate Properties [Line Items]        
Initial basis 5,292      
Cost capitalized subsequent to acquisition 1,813      
Basis at close of period, land 7,029      
Basis at close of period, building and improvements 76      
Basis at close of period, leasehold interests 0      
Total 7,105      
Accumulated depreciation 0      
Book value 7,105      
Development land, related debt 0      
Development Land | New Market, New Market, MD        
Real Estate Properties [Line Items]        
Initial basis 2,088      
Cost capitalized subsequent to acquisition 286      
Basis at close of period, land 2,374      
Basis at close of period, building and improvements 0      
Basis at close of period, leasehold interests 0      
Total 2,374      
Accumulated depreciation 0      
Book value 2,374      
Development land, related debt 0      
Development Land | North Glebe Road, Arlington, VA        
Real Estate Properties [Line Items]        
Initial basis 52,067      
Cost capitalized subsequent to acquisition 6,080      
Basis at close of period, land 0      
Basis at close of period, building and improvements 58,147      
Basis at close of period, leasehold interests 0      
Total 58,147      
Accumulated depreciation 0      
Book value 58,147      
Development land, related debt $ 0      
[1] Includes the North and South Blocks and Residential